Complete the following tasks to unlock the corresponding achievement. To view your achievements and stats in Steam, select "Community", then "My profile", then "View all my games", then the game and view stats.
A Personal Touch: Modify a weapon.
Almost There: Reach Level 15 in multiplayer or level 50 in single-player
Always Prepared: Obtain two noncustomizable suits of armor.
Arbiter: Win a political standoff
Battle-Scarred: Promote a multiplayer character to the Galaxy at War or import an ME3 character.
Bringer of War: Chase down an assassin.
Bruiser: Kill 100 enemies with melee attacks.
Combined Arms: Perform any combinations of 50 biotic combos or tech bursts.
Defender: Attain the highest level of readiness in each theater of war.
Driven: Return to active duty
Enlisted: Start a character in multiplayer or customize a character in single-player.
Executioner: Defeat an old adversary.
Explorer: Complete three multiplayer matches or five N7 missions.
Eye of the Hurricane: Kill a brute while it's charging you.
Fact Finder: Discover an enemy's monstrous origin.
Focused: Evolve any of your powers to rank 6.
Giant Killer: Defeat a Harvester
Gunsmith: Upgrade any weapon to level 10.
Hard Target: Call down an orbital strike.
Hijacker: Hijack an Atlas mech.
Insanity: Finish the game on Insanity without changing difficulty after leaving Earth.
Last Witness: Extract ancient technology
Legend: Mission accomplished.
Liberator: Stop a Cerberus kidnapping
Long Service Medal: Complete Mass Effect 3 twice or once with a Mass Effect 2 import.
Lost and Found: Dispatch 10 probes to retrieve people or resources in Reaper territory.
Mail Slot: Kill 10 guardians with headshots from the front while their shields are raised.
Master and Commander: Deliver most of the Galaxy at War assets to the final conflict
Mobilizer: Bring a veteran officer aboard.
Overload Specialist: Overload the shields of 100 enemies.
Paramour: Establish or rekindle a romantic relationship.
Party Crasher: Sabotage a dreadnought.
Pathfinder: Explore a lost city.
Patriot: Make the final assault.
Peak Condition: Reach Level 20 in multiplayer or level 60 in single-player.
Problem Solver: Evacuate a scientific facility.
Pyromaniac: Set 100 enemies on fire with powers.
Recruit: Kill 250 enemies.
Saboteur: Disable a group of fighter squadrons.
Shopaholic: Visit a store in the single-player campaign.
Sky High: Lift 100 enemies off the ground with powers.
Soldier: Kill 1,000 enemies.
Tour of Duty: Finish all multiplayer maps or all N7 missions in single-player.
Tourist: Complete one multiplayer match or two N7 missions.
Tunnel Rat: Survive the swarm.
Untouchable: Escape a Reaper in the galaxy map.
Unwavering: Finish all multiplayer maps on Gold or all single-player missions on Insanity.
Veteran: Kill 5,000 enemies.
Well Connected: Send a warning across the galaxy.
World Shaker: Destroy an Atlas dropped from orbit.